Cenozoic climate change shaped the evolutionary ecophysiology of the Cupressaceae conifers

Abstract

The Cupressaceae clade has the broadest diversity in habitat and morphology of any conifer family. This clade is characterized by highly divergent physiological strategies, with deciduous swampadapted genera-like Taxodium at one extreme, and evergreen desert genera-like Cupressus at the other. The size disparity within the Cupressaceae is equally impressive, with members ranging from 5-m-tall juniper shrubs to 100-m-tall redwood trees. Phylogenetic studies demonstrate that despite this variation, these taxa all share a single common ancestor; by extension, they also share a common ancestral habitat. Here, we use a common-garden approach to compare xylem and leaf-level physiology in this family. We then apply comparative phylogenetic methods to infer how Cenozoic climatic change shaped the morphological and physiological differences between modern-day members of the Cupressaceae. Our data show that drought-resistant crown clades (the Cupressoid and Callitroid clades) most likely evolved from drought-intolerant Mesozoic ancestors, and that this pattern is consistent with proposed shifts in post-Eocene paleoclimates. We also provide evidence that within the Cupressaceae, the evolution of drought-resistant xylem is coupled to increased carbon investment in xylem tissue, reduced xylem transport efficiency, and at the leaf level, reduced photosynthetic capacity. Phylogenetically based analyses suggest that the ancestors of the Cupressaceae were dependent upon moist habitats, and that drought-resistant physiology developed along with increasing habitat aridity from the Oligocene onward. We conclude that the modern biogeography of the Cupressaceae conifers was shaped in large part by their capacity to adapt to drought.cavitation resistance | photosynthesis | plant water transport | xylem structure

The Structure and Function of Xylem in Seed-Free Vascular Plants: An Evolutionary Perspective

“…Recent phylogenetic approaches have revealed compelling trends in fern diversity that largely point to the post-Cretaceous speciation and radiation of epiphytic taxa. Global climatic shifts may have contributed to this pattern: recent studies of adaptive radiations in monocot, succulent and arid-adapted conifer lineages are consistent with Cenozoic aridifi cation (Edwards et al 2010 ;Arakaki et al 2011 ;Pittermann et al 2012 ). However, equally relevant are several analyses that suggest diversifi cation of fern epiphytes occurred in response to the expansion of complex, angiosperm-dominated forests (Schneider et al 2004 ;Schuettpelz and Pryer 2009 ;Watkins and Cardelus 2012 ).…”

The effect of subambient to elevated atmospheric CO2 concentration on vascular function in Helianthus annuus: implications for plant response to climate change

“…The hydraulic coordination of leaf gas exchange and xylem conductivity and anatomy has been well documented in angiosperms and gymnosperms (Meinzer & Grantz, 1990;Brodribb & Feild, 2000;Santiago et al, 2004;Brodribb et al, 2007;Pittermann et al, 2012), but our study is the first to show that CO 2 forcing can elicit a similar, plastic response that synchronizes hydraulic supply with demand. In H. annuus, conduit diameter varied concurrently with both hydraulic capacity and leaf-level demand for water, whereby plants grown at 290 ppm exhibited a developmental trend towards larger diameter vessels (Fig.…”

“…Indeed, the coordination between leaf-level water loss and the xylemmediated water supply has been demonstrated across both conifer and angiosperm taxa from tropical to temperate environments (Meinzer & Grantz, 1990;Brodribb & Feild, 2000;Santiago et al, 2004;Brodribb et al, 2007;Pittermann et al, 2012). One might expect similar hydraulic coordination from plants growing under a range of [CO 2 ] atm regimes, where under equivalent intensities of light, nutrients and hydration, it is [CO 2 ] atm that drives the hydraulic response through a top-down effect on leaf water loss via stomatal function (Pittermann, 2010).…”

Hemisphere-scale differences in conifer evolutionary dynamics

“…Trees living in Southern Hemisphere temperate forests are not as cold tolerant as many Northern Hemisphere temperate species (4,39), and most southern conifers prefer relatively wet environments (10, but also see ref. 40). The Southern Hemisphere clearly experienced major climatic shifts over the Cenozoic, particularly the spread of open, dry environments in the late Neogene (41)(42)(43).…”